Morphological inspection method based on skeletonization

ABSTRACT

A morphological inspection method based on a comparison of real images—a real reference image and a real inspected image of an inspected object is disclosed.

FIELD OF THE INVENTION

The present invention relates to a morphological tracking method. More specifically, the present invention relates to an inspection method that is useful in automatic inspection.

BACKGROUND OF THE INVENTION

Defects in the form of structural flaws, process residues, and external contamination occur during the production of semiconductor wafers. Defects are typically detected by a class of instruments called defect scanners. Such instruments automatically scan wafer surfaces and detect optical anomalies using a variety of techniques. The location of these anomalies with respect to the pattern of semiconductor devices on the wafer surface is recorded. This information, or “defect map,” is stored in a computer file and sent to a defect review station.

Using the defect map to locate each defect, a human operator observes each defect under a microscope and characterizes each defect according to type (e.g., particle, pit, scratch, or contaminant). Information gained from this process is used to correct the source of defects, and thereby improve the efficiency and yield of the semiconductor production process. Unfortunately, people are relatively slow and are quickly fatigued by the highly-repetitive task of observing and characterizing defects.

Methods of automatically characterizing defects, collectively known as Automatic Defect Characterization (ADC) or Automatic Optical Inspection (AOI) have been developed to overcome the disadvantages of manual defect characterization.

One of the well-known algorithms that is used by AOI systems is a skeleton comparison algorithm. This algorithm skeletonizes the objects of both images—the reference image and the inspected image—and compares the skeletons' junctions and the skeletons' ends in both of the two skeleton images. Skeletonization must be done in real time and in the inspection station. Moreover, the skeletonization process requires a lot of computing source. Consequently, the main disadvantage of these inspection systems is that they are complicated and expensive.

It would be advantageous to have a method and a system, which once skeletonize objects of a reference image and compare this skeletonized image with a real image of the inspected object. This method reduces significantly the costs of the inspection scanners that intend to supply only a real image without real time sketetonization. Moreover, another computer wherein the processing time is not very critical can do the process.

SUMMARY OF THE INVENTION

The present invention is a morphological inspection method based on a comparison of real images—a real reference image and a real inspected image of an inspected object.

According to the teachings of the present invention there is provided an inspection method based on a comparison of real images, made of the following steps:

-   -   creating a reference mask that contains a first color image and         a second color image. The first-color image is obtained from         skeletonization of the reference real image, having a skeletons         image and the second-color image is obtained from         skeletonization of an inversion of the reference image, having         an edges-skeleton image;     -   painting the inspected image in a third color and performing         logical functions using the first-color image and the         third-color inspected image, having a first-defects-image, then         performing logical functions using the second-color image and         the third-color inspected image, having a second-defects-image;         and     -   combining the first-defects-image with the second-defects-image,         having a defects-image or defects-map.

By another aspect of the present invention it is provided the inspection method, wherein at least one region-of-interest is defined, according to inspection criteria, in the reference image and in the inversion of the reference image—wherein the objects that are not inside the regions of interest are ignorable—and each of the skeletinizations ignore the ignorable objects.

By yet another aspect of the present invention it is provided the inspection method, wherein skeletons of the first-color image and the second-color image are trimmed in a way that ignorable defects are not appearing in the defects-image or the defects-map when performing the logical functions.

BRIEF DESCRIPTION OF THE FIGURES

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the figures:

FIG. 1 illustrates a mask preparation, according to the present invention.

FIG. 2 illustrates the inspection process.

FIG. 3 illustrates a flow chart of the method.

DETAILED DESCRIPTION

The present invention is a morphological inspection method based on a comparison of real images.

According to the method of the present invention, defining regions of interest on a first-color image of the inspection reference object. The non-defined regions are ignorable. Then, skeletonizing the image having a first-color image. In the next step, inversing the inspection reference object image and changing its color. Defining regions of interest and skeletonizing the image, having a second-color image of the objects edges. The first-color image contains skeletons of the interest objects, while the second-color image contains edges of the interest objects.

In the inspection process, comparing a third-color image of the inspected object, with the first-color image. This comparison marks the defects of objects' shape. Then, comparing the third-color image of the inspected object, with the second-color image. This comparison marks the defects of objects' edges. By adding these two images, having a defects image.

The principles and operation of the method according to the present invention may be better understood with reference to the drawing and the accompanying description.

Referring now to the drawing, FIG. 1 illustrates a mask preparation, according to the present invention. A first-color real image 11 is used as a reference for inspection. The first-color image 11 contains objects 13 for inspection and an ignorable object 14. Preferring an inverse image 12, which is the inverse of the first-color image 11, but in a second color. Identifying regions of interest 15 on both images 11 & 12 and performing skeletonization on both images while ignoring ignorable objects that are located out of the defined regions of interest. As a result, having two images, a skeletons image (first color image) 16 contains skeletons 19 of the interested objects and an edge-skeletons image (second color image) 17 contains skeletons 20 that are the edges of the interested objects. The two images, the skeletons image 16 and the edge-skeletons image 17, are used as a reference mask 18.

FIG. 2 illustrates the inspection process. The image 21 is the inspected image—obtained from an inspection scanner—contains interested images with a defect 23 a (disconnection) in one object and another defect 23 b (over-splay) in another object. In addition, the image contains an ignorable object 24. The inspected image 21 is compared with the reference mask 18 first, by performing logical function using the inspected image 21 and the skeletons image 16 of the reference mask 18 and second, by using the inspected image 21 with the edge-skeletons image 17 of the mask 18. As a result, having a defects image 22, which contains the first defect (disconnection) 22 a, which is recognized by the skeletons-image 16 and a second defect (over-splay) 22 b, which is recognized by the edges-skeleton image 18. Since non-interested objects are not located in the regions of interest, the ignorable object 24 dose not appears in the defects image 22.

FIG. 3 illustrates a flow chart of the method when inspecting an object, e.g. wafer. Transferring CAD data 25 of a wafer into a wafer image 26 and inversing the image into an inverse wafer image 27, each in different colors. Marking regions of interest 28 in both images. Performing skeletonization of both images, having a skeletonize image 29 of the wafer and a skeletonize image of the inversion 30. Adding 31 both images into a reference mask 32. The inspection process is done by performing logical function 33 using an inspected wafer image 34 and each of images of the reference mask, having a defects image 35 or defects file.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art, accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 

1. A morphological inspection method based on a comparison of real images—a real reference image and a real inspected image of an inspected object—said method comprising: a) creating a reference mask, said reference mask is comprised a first-color image and second-color image wherein: i) said first-color image is obtained from skeletonization of said reference real image, having a skeletons image; and ii) said second-color image is obtained from skeletonization of an inversion of said reference image, having an edges-skeletons image; b) painting said inspected image in a third color and: (i) performing logical functions using said first-color image and said third-color inspected image, having first-defects-image; and (ii) performing logical functions using said second-color image and said third-color inspected image, having second-defects-image; and c) combining said first-defects-image with said second-defects-image, having an inspection-defects-image or defects-map.
 2. The method of claim 1, wherein at least one region of interest is defined, according to inspection criteria, in said reference image and in said inversion of said reference image—wherein object that outside of said regions of interest are ignorable—and each of said skeletinizations ignores said ignorable objects.
 3. The method of claim 1, wherein skeletons of said first-color image and said second-color image are trimmed in a way that ignorable defects are not appear in said defects-image or said defects-map when performing said logical functions. 